In various oil and gas operations, it is desirable or even necessary to operate tools that are located in a wellbore drilled from the surface that penetrates a hydrocarbon bearing formation. Such operations can include opening or closing valves, activating or deactivating tools, and the like. Historically, a variety of techniques have been developed to perform such operations. One example is pressure actuation, in which the pressure in the wellbore can be manipulated by pumps at the surface to induce a desired action. In another variation, plugs, balls, darts, and the like can be dropped into a wellbore or a tubular disposed therein, eventually seating on a mechanism that performs the desired operation. With the development of ever more sophisticated tools and wellbore environments, other actuation techniques have been developed, including the use of Radio Frequency Identification Transponders, also known as RFID tags.
One example of a downhole tool arrangement actuated by an RFID tag is disclosed in applicant's co-pending published U.S. patent application bearing publication number 2014/0305662, which is hereby incorporated by reference in its entirety. In general, this and other RFID embodiments operate by designing a downhole RFID receiver into the tool. This RFID reader will respond to an RFID tag encoded with the appropriate data payload to actuate the tool. When it is desired to actuate the tool, one or more RFID tags having the appropriate data payload can be introduced into the wellbore and, upon arrival at the RFID reader of the tool, will cause actuation of the tool. In some embodiments, the RFID reader and downhole tool can be configured for further actuation or reversal of actuation when an RFID tag encoded with a different corresponding data payload is detected. In such cases, when it is desired to further actuate or reverse the actuation of the tool, and RFID tag can be introduced into the wellbore or a tubular thereof.
RFID tags come in two broad categories. Active RFID tags have their own power source, typically a battery, and are typically configured to continuously transmit their data payload. When they come within range of an Active RFID detector, which can be configured as a “listen only” device, the Active RFID detector will detect the transmitted signal and respond according to its program. Passive RFID tags do not have their own power source, and are powered by a passive RFID tag reader. Generally, a passive RFID tag reader emits a relatively high frequency electromagnetic field (VHF band). This field stimulates a coil in the passive RFID tag that then charges a capacitor within the passive tag that serves as the passive tag's power source. Once the capacitor is charged, the passive tag begins transmitting its payload (typically in the LF band) until the charge in the capacitor is depleted. This transmitted signal is detected by the passive RFID tag reader.
In some embodiments it may be desirable to use an active tag versus a passive tag. The reasons for this can vary. One distinction between commercially available active and passive tags is operating frequency. Heretofore, passive tags used in downhole tool operation have typically operated in the LF range, while most commercially available active tags operate in the UHF range. Also, many passive tags operate using FM (frequency modulated) or FSK (frequency shift keying) while many commercially active tags operate using AM (amplitude modulated) or ASK (amplitude shift keying) for encoding data. Also, many active tags and/or active tag readers are not designed to accommodate the high operating temperatures, pressures, and vibration levels associated with downhole operation. Finally, there is an existing base of downhole tools that are designed around various existing passive reader technologies, and adapting these to conventional active tags would require significant redesign of antennas, transceivers, and the like. Thus, what is needed is a mechanism to adapt preexisting passive RFID tags for active mode operation or to otherwise simulate the operation of such preexisting RFID tags with an active RFID tag design.